omics-scatac

name	omics-scatac
description	Single-cell ATAC-seq — fragment import, ATAC QC (TSS / fragment-size / FRiP / doublets), feature matrix (tiles / MACS3 peaks), spectral (LSI) clustering, motif activity (chromVAR), gene activity, peak–gene linkage, scRNA label transfer.
requiredTools	["run_python","create_notebook","add_cell","observe_figure","omics_preflight","omics_runtime"]
evidencePolicy	required
outputSchema	grounded_response
minConfidence	medium
tags	["omics","scatac","single-cell","chromatin","accessibility","snapatac2","chromvar","muon"]
extends	omics-shared

scATAC-seq Analysis

Builds on omics-shared (loaded automatically — its rules apply here). Run compute through the omics_runtime tool with modality="scatac"; it dispatches into the pinned task4 env and records evidence automatically. Steps without a subcommand are hand-rolled in run_python with snapATAC2 (and pychromVAR for motifs) — read the method doc first.

Prerequisites

1. omics_preflight(modality="scatac") passes (validates task4: snapATAC2 + MACS3).
2. A fragments file (fragments.tsv.gz + .tbi) for QC / peak calling, or a pre-built cell×peak/tile AnnData.
3. A summarize report + free-text study description threaded into every biological decision.

Capability menu (with maturity)

Capability	Maturity	How	Method doc
Import fragments → cell×feature matrix	REFERENCE	snapATAC2 pp.import_fragments	method/import_fragments.md
ATAC QC (TSS, fragment size, FRiP, doublets)	READY	omics_runtime atac_qc	method/atac_qc.md
Feature matrix (tiles / peaks)	PARTIAL	snapATAC2 tiles; peaks via peak_calling	method/feature_matrix.md
Peak calling (MACS3, per-cluster)	READY	omics_runtime peak_calling	method/peak_calling.md
Spectral (LSI) embedding + Leiden	REFERENCE	snapATAC2 tl.spectral / tl.leiden	method/dimred_cluster.md
Motif activity (chromVAR)	REFERENCE	pychromVAR	method/motif_enrichment.md
Gene activity scores	READY	omics_runtime gene_activity	method/gene_activity.md
Peak–gene linkage (co-accessibility)	REFERENCE	distance + correlation (muon)	method/peak_gene_linkage.md
Label transfer / integration from scRNA	REFERENCE	gene-activity bridge + scRNA recipes	method/rna_integration.md

Read the method doc before running a capability — each gives the opinionated default, exact parameters, failure modes, and grounding.

GRN inference is not a pure-scATAC step. It needs expression: for TF regulons use scRNA (omics-scrna, pySCENIC); for enhancer-driven GRN use multiome (omics-multiome, SCENIC+). Do not infer a GRN from accessibility alone.

Standard workflow

Run each step through omics_runtime where a subcommand exists; otherwise hand-roll per the method doc. Read the per-step doc for parameters and decisions.

1. Preflight & import — omics_preflight(modality="scatac"); import the fragments file into a snapATAC2 AnnData (method/import_fragments.md); omics_runtime(subcommand="summarize", modality="scatac", args={"input":"atac.h5ad"}). Thread the summary + study description forward.
2. ATAC QC — omics_runtime(subcommand="atac_qc", modality="scatac", args={"input":"atac.h5ad","output":"qc.h5ad","fragment-file":"fragments.tsv.gz","compute-tsse":"true","compute-frip":"true","filter":"true"}). See method/atac_qc.md for TSSE / nucleosome / FRiP thresholds and the MAD-vs-fixed decision.
3. Feature matrix — tile matrix for a first pass, or call peaks per cluster: omics_runtime(subcommand="peak_calling", modality="scatac", args={"input":"qc.h5ad","output":"peaks.bed","fragment-file":"fragments.tsv.gz","mode":"pseudobulk","cluster-column":"leiden"}) (method/feature_matrix.md, method/peak_calling.md).
4. Embed & cluster — snapATAC2 spectral (LSI) embedding, then Leiden on obsm["X_spectral"]; drop the depth-correlated first component (method/dimred_cluster.md). Plot UMAP and observe_figure.
5. Gene activity — omics_runtime(subcommand="gene_activity", modality="scatac", args={"input":"qc.h5ad","output":"gene_activity.h5ad"}) for an expression proxy used in annotation / integration (method/gene_activity.md).
6. Motif activity (chromVAR) — per-cell TF motif deviations via pychromVAR (method/motif_enrichment.md).
7. Linkage / integration (as needed) — peak–gene links (method/peak_gene_linkage.md); label transfer from an scRNA reference via the gene-activity bridge (method/rna_integration.md).
8. Visualize & ground — plot UMAP colored by clusters / QC / gene-activity markers; observe_figure each before it backs a claim; cite the omics_runtime reports as evidence.

scATAC-specific rules (on top of omics-shared)

• TSS enrichment is the primary QC axis — always compute + report TSSE when a fragments file is present, and gate filtering on it (method/atac_qc.md).
• Spectral (LSI), not PCA — ATAC is sparse / near-binary; use snapATAC2 spectral embedding and drop the depth-correlated first component (method/dimred_cluster.md).
• Accessibility ≠ expression — gene activity is a proxy; validate it against markers and say so; never report it as measured expression.
• Distance ≠ regulation — a peak near a gene is a hypothesis, not a regulatory link; ground linkage claims and abstain when correlation is weak (method/peak_gene_linkage.md).
• Abstain over guess — an ambiguous cluster is "unknown", not an invented label.

When things go wrong

• TSSE low across all cells — library quality or wrong genome annotation; check the fragments file + genome build before filtering (method/atac_qc.md).
• Clusters track total counts / TSSE — technical variation dominates; revisit feature selection or drop the first spectral component (method/dimred_cluster.md).
• Too few peaks after calling — pseudobulk per cluster has too few cells, or the q-value is too strict; aggregate more cells or relax (method/peak_calling.md).
• Gene activity is noisy — expected for a proxy; smooth over neighbors or restrict to confident peak–gene links; do not over-interpret single genes.